The fact that electric water heaters manufactured have quick recovery heating elements installed in them has caused serious problems to the industry.
Safety codes require that at the time of installation a temperature and pressure relief valve be installed on each water heater with a maximum opening pressure of 150 PSI. Since the element heats the water at a very rapid pace, the water will expand rapidly and cause the pressure in the heater to exceed the opening pressure of the relief valve, thus causing the relief valve to discharge hot water. This can be very wasteful and also very dangerous.